Since this novel is basically one long thought experiment about personal identity, I figured I'd skip right to the Philosophy Report section of the review. See my regular review of stuff like the writing and the plot on Goodreads.
Anyone who's read John Locke on personal identity will recognize this one (curiously, Sawyer himself doesn't mention Locke, but there are a few pages on John Searle's Chinese Room thought experiment, so he's doing pretty well for a non-specialist).
What if your mind was copied into another body? Would that other you still be you? Would there be two yous, or just one real you and one fake "you"?
Okay, now what if you could pay a company to copy your mind into a robot body that looked like you? And just to keep things from getting too complicated, say you do this toward the end of your life and you (i.e., the original, biological you) retire permanently to the dark side of the moon (but not in the Bladerunner sense of "retire"; whether you listen to Pink Floyd up there is up to you). Meanwhile, the new you (i.e., the artificial one) stays on Earth with all your legal rights where the new you will live, perhaps for hundreds of years or more, and do all the things that a basically immortal you wants to do.
That's the story of Mindscan. You can find similar ideas in a book I read over 20 years ago, but that has always stayed with me: Mind Transfer by Janet Asimov. And of course in the cheesy, but surprisingly deep, Arnold Schwarzenegger movie The Sixth Day.
Mindscan is a fun story with some real live cognitive science and philosophy sprinkled throughout, especially during a dramatic trial in which the son of one of the "Mindscans" claims that he should receive his inheritance after the original, biological version has died. (The trial reminded me of the Star Trek: The Next Generation Episode called "The Measure of a Man" in which Data is put on trial to prove that he's not merely Starfleet property - I used to show this episode in my Intro to Philosophy classes). The philosophy isn't always handled with professional rigor you'd get from a specialist (the philosophy PhD who takes the stand in the trial is pretty weak), but then most philosophers don't know how to write a good story, so you've got to give Sawyer a break. The other big part of the plot revolves around the original, biological version of a Mindscan coming to believe he made a mistake (I don't want to spoil too much, so I won't say what prompts him to think so).
I loved the way that Sawyer wrote the points of view of both versions of the main character in the first person. Perhaps because of my Buddhist influences and appreciation of Locke's psychological continuity criterion, I don't have any real problem with declaring that both versions are "the real me." According to Locke, if both versions have your memories and some psychological continuity, then they're both you (in later literature, people started calling this a fission thought experiment). For most Buddhists, there is no ultimately real thing called "you" - "you" are a conventionally-designated set of physical and mental processes that it's handy to call "you." So why not make two of those conventionally-designated "yous"?
Of course, having two yous makes things complicated. Do you both have to go to the DMV? Are you both married to your spouse? Could one you go on vacation without using vacation time if the other you stayed at work? How much faster could two of you clean the house? Hopefully by the time weird stuff like this happens (if it ever happens), philosophers and science fiction writers will have figured it out.
In the meantime, the real point of thought experiments like this is to explore the conceptual space in which our concepts of personal identity live. This comes in handy in some of the thorniest real life cases out there: what to do with individuals in persistent vegetative states, whether apes or dolphins should have rights, abortion, euthanasia, Alzheimer's patents or others with severe loss of memories and/or cognitive skills, etc.
In so far as Sawyer presents a fun and dramatic version of a fission personal identity thought experiment, this is well worth a read.